A former longtime Jasper Johns assistant was ordered Thursday to spend 18 months behind bars after admitting he stole artworks from the pop artist's Connecticut studio and arranged for them to be sold by a Manhattan gallery for nearly $10 million.

James Meyer, 53, of Salisbury, Connecticut, was also ordered to pay $13 million in restitution and to forfeit $3.9 million.

U.S. District Judge J. Paul Oetken said he believed Meyer was genuinely remorseful and was primarily a "kind, caring, thoughtful" man who committed a serious offense, selling unauthorized artworks on at least three occasions from 2006 to 2011, pocketing more than $4 million.